sessiel

Sessiel is an adjective used in Dutch to describe something that is fixed in place, attached to a substrate, and lacking mobility. The word derives from Latin sessilis, from sedere, meaning to sit. In English, the closest equivalent is sessile. The term is used across biology and medicine to describe objects or structures that are attached directly by their base without a stalk and do not move on their own.

In biology, sessile describes both organisms and plant parts. In zoology, sessile organisms remain attached to a surface for at least part of their life cycle, such as barnacles, corals, sponges, and many stationary colonial organisms. In botany, a sessile leaf or flower is attached directly to the stem without a petiole or stalk. Sessility is often contrasted with motility or with structures that are pedunculated, meaning attached by a slender stalk.

In medicine, sessile is used to characterize lesions, tumors, or polyps that have a broad base and are attached directly to tissue, rather than being supported by a long stalk (pedunculated). This distinction can influence diagnostic assessment, treatment planning, and surgical approach. For example, sessile polyps may require different resection techniques compared with pedunculated lesions.

Related terms include sessility, referring to the state of being sessile. The concept of sessility helps describe attachment, orientation, and growth form across biological and medical contexts.